processes: increase reading buffer for /proc/stat

processes: increase reading buffer for /proc/stat

If machine has high number of CPUs or interrupts or both, the /proc/stat
can easily grow over current buffer size 4kB. On my current machine (64
cores, ~300 interrupts) the /proc/stat has 12kB of data. And since the
`procs_running` line is after the interrupts it is never read.

Increasing the size to 64KB so it will accommodate even heavier machines.